A voltage follower, also known as a buffer circuit, is a simple electronic circuit designed to replicate an input voltage at its output while providing a high input impedance and a low output impedance. In other words, it "follows" the input voltage, maintaining the same voltage level but with the ability to supply more current if needed. The main purpose of a voltage follower is to isolate or decouple circuits with different impedance levels, preventing loading effects and signal degradation.
The basic configuration of a voltage follower circuit involves using an operational amplifier (op-amp) with a feedback loop that connects the output of the op-amp back to its inverting (-) input terminal. The non-inverting (+) input of the op-amp is connected to the input voltage source. The output of the op-amp is then taken from its inverting input, which is virtually at the same voltage level as the non-inverting input due to the feedback loop.
Key characteristics and advantages of a voltage follower circuit:
High Input Impedance: The input impedance of a voltage follower is typically very high, approaching the ideal value of infinite impedance. This means that the circuit draws negligible current from the input source, effectively isolating the source from the following circuit.
Low Output Impedance: The output impedance of a voltage follower is quite low, which allows it to supply current to the following circuit without causing significant voltage drop due to internal resistance.
Unity Gain: The voltage gain of a voltage follower is very close to unity (gain of 1). This means that the output voltage closely matches the input voltage, making it useful for voltage level shifting or impedance matching applications.
Applications of Voltage Follower (Buffer) Circuit:
Impedance Matching: When connecting a signal source with a relatively high output impedance to a load with a low input impedance, a voltage follower can be used to match the impedances and prevent signal loss.
Instrumentation Amplifiers: Voltage followers are often used as buffer stages in instrumentation amplifier circuits, which are commonly used in precision measurement applications.
Voltage Level Shifting: When you need to shift the voltage level of a signal without changing its shape or waveform, a voltage follower can be used.
Isolation: Voltage followers can help isolate one stage of a circuit from another. This is particularly important when you want to avoid affecting the behavior of one stage due to the characteristics of another stage.
Driving Low Impedance Loads: When a signal source has limited current-driving capability and needs to be connected to a low impedance load, a voltage follower can provide the necessary current drive.
Buffering Sensitive Devices: Sensitive devices that can be affected by loading effects, such as sensors, can be connected to a voltage follower to prevent interference.
In summary, a voltage follower (buffer) circuit is a versatile tool in electronics that helps prevent loading effects, maintain signal integrity, and match impedance between different stages of a circuit.